When a vehicle is initially started (a cold start), an engine and an intake system have low temperatures, and heat loss in the engine leads to lower fuel efficiency.
In order to improve this, an engine preheating apparatus in which an electrothermal air heater is installed to be adjacent to an inlet of an intake manifold to preheat intake air having a temperature equal to or lower than a predetermined temperature has been presented.
However, in the engine preheating apparatus using an electrothermal air heater as described above, an installation of the air heater requires an installation layout around an engine, degrading assembly characteristics, and in particular, requires a separate power source which may degrade overall fuel efficiency of a vehicle.